[unreadable] The overall goal of the proposed research is to characterize the effects of repeated exposure to the amphetamine derivative, MDMA (ecstasy), on behavior, striatal single-unit electrophysiology, and striatal dendritic morphology after relatively long withdrawal periods. Specifically, we will analyze the activity of striatal neurons in freely moving rats following a one-month withdrawal period from repeated MDMA administration and a subsequent challenge injection of MDMA. Because a change in DA receptor functioning is one of the many adaptations that occur after repeated exposure to AMPH-like stimulants, we will combine dopamine D1 or D2 antagonist administration with the challenge injection of MDMA. Finally, to assess the relatively long-term effects of MDMA on the structure of striatal neurons, we will use the Golgi method to examine the dendritic morphology of striatal medium spiny neurons following one month of withdrawal from repeated MDMA administration. The role for striatum in the acute behavioral effects of MDMA, combined with the potential role for striatum in the transition to drug addiction indicate that these types of studies will provide valuable insight into the neural mechanisms of MDMA use and abuse. [unreadable] [unreadable] [unreadable] [unreadable]